The renin-angiotensin system is being investigated in neural tissue in several ways. The distribution of renin is to be investigated by immunocytochemistry in rat and mouse brain, particularly in vasopressin neurons of rat hypothalamus which have been shown previously to contain immunoreactive angiotensin II. The angiotensin II reactive substance is being extracted from these cells and chromatographed. Also, by immunocytochemistry angiotensin II is being studied in vasopressin projections from the paraventricular nucleus of the rat hypothalamus to various other brain sites including spinal cord.